Pressure minesweeping



Dec. 12, 1961 c. s. THOMAS 3,012,534

PRESSURE MINESWEEPING Filed July 16, 1954 I INVENTOR Char/es .5. ThomasATTORNEYS 3,012,534 Patented Dec. 12., 1961 ice 1 3,012,534 PRESSUREMINESWEEPING Charles S. Thomas, San Diego, Calif. Mare Island NavalShipyard, Vallejo, Calif.) Filed July 16, 1954, Ser. No. 443,978 3Claims. (Cl. 114-435) (Granted under Title 35, US. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to the sweeping of pressure responsive mines andmore particularly to a method and apparatus for producing within a mineinfested body of water pressure variations of the type and pattern towhich the mines are supposedly responsive.

Pressure responsive mines, hereinafter referred to simply as pressuremines, are provided with an actuating mechanism which is responsive to apredetermined reduction within a limited time interval in the pressureof the surrounding water functions to detonate the mine. Pres sure minesare usually provided with an electroresponsive detonator operativelyconnected to a firing circuit adapted to be closed when the reduction inpressure of the water has been continually maintained for apredetermined limited period of time so as to prevent prematuredetonation by pressure variations which might result from the action ofwaves as well as to prevent detonation by slow, long term variations ofpressure such-as result from tides and seiches. These operative pressurerequirements are met for the purpose of providing an actuating mechanismwhich is selectively responsive to pressure changes such as are inducedby the passage of a large vessel through a seaway, such pressurevariations when plotted against time being commonly referred to as apressure signature. Some pressure mines are designed so, as to requirefor actuation an accessory signal; usually magnetic or acoustic.

The primary desideratum in pressure minesweeping can thus be saidtoamount to no more than counterfeiting the pressure signature of thetype ship for which the mines are designed with means other and lessvaluable than such ship, the production of the accessorysignal beingrelatively simple. Ideally, of course, the minesweepers should be ableto actuate and thus destroy a mine without being damaged in the process.Also, since areas that are mined are frequently restricted it is highlydesirable that the minesweeping gear employed be readily maneuverable.

In accordance with the present invention a pressure signaturecorresponding to a large vessel is produced by a device whose physicalbulk is considerably less than that indicated by its pressure signature.This may be achieved by producing in the water a horizontal flow ofwater transversely confined for a fixed length and advancing thisconfined flow of water in the direction of the flow, the arrangementbeing such that the flow of water creates a source and sinkdiscontinuity, several times larger in cross section than the crosssection of the flow confining means, which when moved through the waterat a constant speed produces the desired uniform moving field forcreating in terms of pressure and flow lines the effect of a solid bodymoving through the water. I

An object of the invention is the provision of a new and improved methodand apparatus for sweeping pressure responsive marine mines.

Another object of the invention is the provision of apparatus forsimulating under water the pressure signature of a moving vessel.

A further object of the invention, is to provide afpressure-mine sweepwhich can be controlled while in use to'simulate selectively thepressure signature of ships of different sizes.

Still another object of the invention is the provision of a method forproducing large-ship pressure signatures with a relatively small device.

Another object of the invention is the provision of a device whichproduces underwater pressure changes accompanied by an accessory signalor signals for sweeping mines having actuators responsive only tomultiple influences.

Another object of the invention is the provision of a pressure-minesweep which is so designed and constructed as'to be relatively immune todamage from the explosion of a swept mine.

The invention itself, as well as other objects and advantages thereof,will become manifest fromthe following description of specificembodiments thereof when read in connection with the accompanyingdrawing and its scope will be pointed out in the appended claims.

In the drawing:

FIG. 1 is a side elevation partly in section of a mine sweepingapparatus according to the invention;

FIG. 2 is a side-view of an alternative embodiment of the invention;

FIG. 3 is a section taken along the line 33 in FIG. 2; and 1 FIG. 4shows sweep units connected in cascade being towed through water.

As shown in FIG. 1 a circular hollow cylinder or'tube 10 .is providedwith a propeller type pump 11 adapted to be driven by suitable motivepower such as an electric motor 12, mounted axially in the tube 10 bymeans of diametrically extending spars or spiders 13 for pumping waterthrough the tube 10 in the direction indicated by arrows 14. The tube 10may be supported at the desired level below the water surface bysuitable buoys 15 and moved through the water by a towing line 16 in awellknown manner. When the pump driving means 12 is an electric motor,power may be supplied thereto through a suitable flexible currentcarrying member 17 which preferably is married to the tow cable 16 asindicated. -It is to be understood that the pump means employed is notimportant to the invention as long as the desired volume of water iscirculated through the tube 10 in the direction it is tobe towed throughthe water. As indicated by the flow lines 18 the water pumped throughthe tube '10 tends to recirculate as in a closed system, and when thetube 10 is moved longitudinally through a body of water in the directionin which the water is flowing in the tube 10 it creates, at least forpressure minesweeping purposes, the effect of a solid body having aconsiderably larger cross section than the physical cross section of thetube 10. Without referring to strict theory of rigorous proof, itis-believed to be reasonably accurate to say that this greatly increasedeffective cross section is brought about somewhat as follows:

The couplet (i.e., closely adjacent source and sink) normally appearingin the vicinity of a propeller operating in the water is expanded by thebaffling effect of the tube 10 so that the source and sink becomeseparated by approximately the length of the tube 10 whereby therecirculating water constitutes closed streamlines 18 around which flowlines 19 are formed, it being well known that a closed streamline and asolid body are interchangeable without affecting the flow, hence themovement of the tube and its satellite body of water having an envelopeindicated by the outermost closed streamline 18 through the waterproduces the same flow, as indicated by the line 19, as would themovement of a solid body of the size and, shape of the closed streamline18.

Since the device functions as a closed system, at any given towing speedthe volume of flow determines the diameter of the discontinuityproduced, i.e., the distance separating the outer streamline 18. Thus,for example, if the tube is made fourteen feet in diameter and towed atsix knots, water pumped through the tube at a velocity of thirty feetper second will create a discontinuity approximately twenty-eight feetin diameter and of a length determined by the length of the tube 10.

If the tube 10 is constructed of paramagnetic material such as iron orsteel it will be evident that in addition to producing the desiredpressure variations the device will simultaneously produce a magneticdiscontinuity which can sweep magnetic mines as well as furnish themagnetic look for pressure mines requiring an accessory magnetic signal.Also, the motor 12 and the propeller pump 11 employed for moving so muchwater will furnish the acoustic look for pressure mines requiring anaccessory acoustic signal. It will also be evident that the power cableleading from the device to the towing vessel may in itself constitute amagnetic sweep.

When sweeping operations are to be conducted in relatively shallow waterthe operating principles described above may be incorporated in a moreefiicient device shown in FIGS. 2 and 3 as comprising a U-shaped channel21 made buoyant by suitable sponsons 22 and provided with means such asa paddle wheel 23 for moving water through the channel 21 in thedirection of tow through a tow cable 24, it being understood that theparticular means employed for moving the water forward through thechannel 21 is unimportant. The paddle wheel 23 may be driven in anysuitable manner as by an internal combustion engine 25 mounted abovewater on the channel sponsons 22 and connected in driving relation tothe paddle wheel 23 by suitable means such as a chain 26 trained oversprockets 27 and 28 carried, respectively, by the output shaft 29 of aspeed reduction gear box 30 connected to the engine 25 and the paddlewheel 23. More specifically, the paddle wheel 23 may be provided withaxially disposed trunnions 31 journaled in bearings 32, suitably mountedon the sponsons 22. The sprocket 28 may be mounted on one of thetrunnions 31 or secured to the side of the paddle Wheel proper. Also,the operation of the internal combustion engine 25 is preferablyremotely controlled from aboard the towing vessel in any suitablewell-known manner.

With this channel arrangement the efficiency is considerably increasedby reason of the fact that the downwardly extending flow, which is themost eifective for producing pressure variations at the water bed, isprimarily employed. In this connection it may be noted that thearrangement shown in FIG. 1 necessarily dissipates a considerable amountof energy in the flow taking place above the horizontal plane defined bythe axis of the tube 10 but this apparent inefficiency can be toleratedor, more accurately, compensated by submerging the device to the optimumdepth, thereby reducing attenuation of the pressure change at therelatively deep water bed. This optimum distance from the water beddepends upon so many variables, including the magnitude of pressurechange needed at the water bed, the rate of attenuation in the water,the nature of the water bed, and the effective area at the water bed itis desired to sweep at each pass, that it must be determined separatelyfor each particular area to be swept.

It being postulated that to sweep a given pressure mine a predeterminedreduction Ap in pressure must be continuously maintained for a period oftime t, it becomes apparent that with the device of the presentinvention the values for Ap and t can be separately varied by alteringthe rate the water is pumped through the device independently of thespeed of tow. The time t varies directly with the towing speed while thevalue of Ap is a function of both the towing speed and the pumping rate;thus, within the operating capabilities of the device and the towingvessel, the pressure signature of any ship can selectively be simulated.

As indicated in FIG. 4, two or more units 33 and 33' may be connected incascade and towed by a surface ship 34 through a suitable cable 35. Thetwo units 33 and 33 as shown are connected in end to end relation bysuitable metal rings or links 36 which preferably provide a limitedamount of play so as to obtain the benefit of a small amount ofarticulation which renders the device less cumbersome to handle. Thiscascade or tandem arrangement, in addition to making it possible toadapt the length of the sweep to suit a particular operating situation,also offers the advantage of making it possible in many cases tolocalize damage resulting from the explosion of a swept mine, it beingobvious that one segment or section can be more readily, as well as lessexpensively, replaced than if the entire unit was an integral mass.Although this cascade arrangement, illustrated in FIG. 4, shows the useof the cylindrical tube form of the device, it will be appreciated thatthe advantages of the cascade arrangement accrue equally well when usingother forms such as the buoyant channel of FIGS. 2 and 3.

The cascade arrangement indicated in FIG. 4 becomes even moreadvantageous if only the forward unit 33 is provided with pumpingapparatus 12 leaving the aft unit 33' to perform merely the function ofconfining the flow of water and therefore inexpensive enough to beconsidered expendable. When this modified arrangement is employed inoperation the sweep can be towed at a speed such that the time t elapsesjust as the rear portion of the aft section 33' passes over a mine, theresult being that a swept mine is exploded beneath or behind the leastvulnerable and most readily replaceable portion of the sweep (Le, aplain confining section containing no pumping equipment). As wasdiscussed above, it is possible to vary the time t with any given sweepsystem while maintaining the desired value for Ap so that in practice,after the critical time t has been ascertained for the mines beingswept, by suitably altering the pumping rate the speed of towing can bechosen to the end that mines when swept will explode at the moment whichis most opportune from the viewpoint of damage to the sweeping gear. Itmight be well to here note that a water filled circular cylindrical tubewholly submerged in water is relatively immune to explosions because theshock waves are transmitted rather than absorbed by the water filledtube, it being a wellknown fact that the portions of a submerged bodysufiering the most damage from underwater explosions are thosecontaining gas filled cavities.

When it is remembered that the pumping action of the water within thesweep exerts a strong driving force opposite the direction of tow thepossibility exists for sweeping restricted blind harbors by simplypermitting the de vice to propel itself in a backward direction into thebarbor and then towing it forward. No other pressure sweep is knownpermitting this sometimes very desirable maneuver.

In describing the invention to enable those skilled in the art tounderstand and practice it, only two embodiments have been illustratedand these only in their essential form since details of fairing,streamlining, finning for dynamic stability, etc., can readily beprovided by those skilled in the art, and any description of suchdetails would serve to obscure rather than make clear the real inventivefeatures constituting the present invention.

Although only the preferred embodiments for two different sweepingoperations .have been described for the purpose of disclosing theinvention, it is to be understood that the invention is not limited tothese particular embodiments but is of the scope indicated in theappended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In the art of submarine pressure minesweeping the method of creatingfor a given interval of time a desired negative pressure on the bottomof a seaway which comprises producing in the seaway a horizontal flow ofwater transversely confined for a fixed distance and advancing this saidconfined flow of water in the direction of said flow at a speed suchthat said fixed distance is traversed in the given interval of time.

2. In the art of sweeping sea submerged mines responsive to a pressurereduction Ap maintained for a time interval t the method which comprisesproducing a transversely confined flow of water between two pointsspaced horizontally a distance d to create in the seaway a source andsink separated approximately by the distance d, advancing said confinedfiow of water in the direction of its flow at a speed substantiallyequal to but no greater than d divided by t, and adjusting the rate offlow in said confined flow as an inverse function of the speed ofadvance, whereby the required reduced pressure Ap may be obtainedindependently of the speed of advance.

3. The minesweeping method in accordance with claim 2 wherein when saidconfined flow of water cannot be advanced the full distance d over anyfixed point on the Water bed or when a running start is impracticable,the

a 6 steps consisting in adjusting the rate of flow from below the rateto the rate at which the reduced pressure Ap is produced and maintainingthis latter rate for at least the time interval t.

References Cited in the file of this patent UNITED STATES PATENTS 39,394Ham's Aug. 4, 1863 321,569 Belus July 7, 1885 717,356 Cunningham Dec.30, 1902 1,310,326 Dibble July 15, 1919 2,353,360 Running July 11, 19442,395,944 Smith Mar. 5, 1946 2,543,253 Napoli Feb. 27, 1951 2,745,370Manis May 15, 1956 FOREIGN PATENTS 5,693 Great Britain -9 940,395 FranceMay 18, 1948 955,055 France June 20, 1949 OTHER REFERENCES ScientificAmerican, October 9, 1915, p. 325.

